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Concerns about the health effects of nitrogen dioxide (NO2) and its role in forming deleterious atmospheric species have made it desirable to have low-cost, sensitive ambient measurements of NO2. We have developed a continuous-wave laser-diode laser-induced fluorescence (LIF) system for NO2 that operates at ambient pressure, thereby eliminating the need for an expensive pumping system. The current prototype system has achieved sensitivity several orders of magnitude beyond previous efforts at ambient pressure (limit of detection of 2 ppb, 60 s averaging time). Ambient measurements of NO2 were made in Portland, Oregon using both the standard NO2 chemiluminescence method and the LIF instrument and showed good agreement (r2 = 0.92).

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To make air quality monitoring accessible to a broad range of people (i.e. consumers, educational groups, and environmental activist) a low-cost method for sampling nitrogen dioxide (NO2) was modeled after the Palmes and Gunnison diffusion samplers. This article describes the results of using cost-effective passive diffusion tubes for measuring NO2 in outdoor environments. Samplers are compared against a collocated chemiluminescence (active) monitor in a gas exposure chamber for concentration of NO2 between 10 and 200 ppb/v (parts per billion per volume). In these calibration experiments diffusion samplers had strong correlation to the active monitor, R2 = 0.94 for a one week sample interval, and a R2 = 0.91 for a two week sample interval. A four week study was conducted with a collocated active monitor and a total of 42 samplers. The samplers were divided into 6 groups and exposed in one week and two week intervals under environmental conditions: temperature 18-31°C, relative humidity 27-57 %, wind speed 0.4-3 m/s, and NO2 concentration 2-22 ppb/v. The precision, calculated as the relative standard deviation, for the one week sample interval was found to be 8.2%, and for the two week sample interval 20.2%. Three cleaning methods of exposed samplers are compared in order to identify bias in reusing components. Using the best cleaning method the mean NO2 absorbance of a dry sampler is 1.3 ± 0.4 ppb/v as opposed to a zero absorbance for unused samplers.

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